Abstract
Slender boiler tubes are subject to localised swelling when they are expose to excessive heat. The latter is due to the formation of an oxide layer, which acts as an insulation barrier. This excessive heat can lead to microstructural changes in the material that would reduce the mechanical strength and would eventually lead to critical and catastrophic failure. Detecting such creep damage remains a formidable challenge for boiler operators. It involves a costly process of shutting down the plant, performing electromagnetic and ultrasonic non-destructive inspection, repairing or replacing damaged tubes and finally restarting the plant to resume its service.This research explores through a model developed using a finite element computer simulation platform the thermal behaviour of slender tubes under constant temperature exceeding 723 °K. Our simulation results demonstrate that hematite layers up to 15 μm thickness inside the tubes do not act as insulation. They clearly show the process of long term overheating on the outside of boiler tubes which in turn leads to initiation of flaws.
Highlights
Boilers and other heavy industrial equipment operating at high temperatures and pressure are design for a finite life [1]
Slender boiler tubes are subject to localised swelling when they are expose to excessive heat
We study the effects of long term overheating due to the formation of oxide layers inside boiler tubes
Summary
Boilers and other heavy industrial equipment operating at high temperatures and pressure are design for a finite life [1]. Our simulation results demonstrate that hematite layers up to 15μm thickness inside the tubes do not act as insulation. The effects of the oxidation layers on the mechanical behaviour of materials manifest themselves in a reduction of the tube cross section, which increases the localised stress.
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